It took days to figure out why Firefox was aborting all requests after my login screen. So, I will make the conclusion of my search bold and underlined:

If you are using Mvc-mini-profiler and only logging to the database, you will eventually come to a time when the number of GUIDs that Mvc-mini-profiler inserts into your HTTP responses (X-MiniProfiler-Id headers) will grow to the point where Firefox will silently drop any requests to your website. Firefox will show GET requests with undefined response codes and refuse to load any further pages from your site until the Mvc-Mini-Profiler is turned off.

The fix for this is to create a custom SqlStorage provider for Mvc-mini-profiler and override the HasUserViewed field. Here is my attempt at this: